It is common to diagnose prostate cancer using transrectal ultrasonography (TRUS) guided needle biopsy procedures. A TRUS guided needle biopsy is often prescribed as a result of an elevated prostate-specific antigen (PSA) level or upon detecting a palpable nodule during a digital rectal exam. Introduction of ultrasound (US) image-guided prostate biopsies substantially increases the accuracy of a prostate biopsy over performing a blind biopsy, thus TRUS guidance has become a universally accepted method for prostate biopsy. While TRUS guided prostate biopsies are a clinically accepted method, the procedures retain a low sensitivity of approximately 60% and positive predictive value of only approximately 25%. Consequently, repeat biopsies are often required. For example, in over 20% of the cancer studies, more than one biopsy session is required for a physician to reach a diagnosis decision.
Three-dimensional visualization applications, such as magnetic resonance imaging (MRI), can clearly depict the prostate gland and prostate substructures, including the central, transitional, and peripheral zones. For example, T2-weighted images can depict nodules in the peripheral zone. Localizing a tumor foci and the peripheral zone with MRI before a prostate biopsy may increase the overall cancer detection rate and the biopsy yield. Additionally, functional information acquired from various MRI techniques, such as diffusion weighted imaging (DWI), dynamic contrast-enhanced (DCE) imaging or chemical shift imaging (CSI), may be used to further characterize the prostatic tumor tissue. Using this functional information during the ultrasound guided biopsy may substantially improve the sensitivity of the biopsy procedure.
For example, endorectal MRI images and findings for suspected tumor foci may be used to manually guide the placement of needles during TRUS guided biopsy. By localizing biopsy to suspected tumor lesions and other targets identified on the endorectal MRI image, the physician may visually correlate the locations in the endorectal MRI image with ultrasound images during a subsequent TRUS guided biopsy, increasing the accuracy of the TRUS guided biopsy to approximately 67%, as demonstrated in a study of 33 patients. However, correlating locations using an MRI image requires a tedious visual inspection.
Robotic arms have been developed for handling ultrasound probes. For example, the robotic arms may alleviate physician fatigue during scanning procedures. In a robotic system, a physician's grasp and input to the ultrasound probe may be detected, such as by a 6-axis force sensor, and multiple detected parameters may be used for compliance control and self-weight compensation of the ultrasound probe as the probe is moved and adjusted by the physician.